swupdate-image: set USE_DEVFS to 1

swupdate relies to devtmpfs. The patch fixes the error by building:

| makedevs: No entry for root in search list

Signed-off-by: Stefano Babic <sbabic@denx.de>

recipes-extended/images/swupdate-image.bb

@@ -18,7 +18,8 @@ IMAGE_INSTALL = "base-files \
 		initscripts-swupdate \
 		 "
 
-
+USE_DEVFS = "1"
+#IMAGE_DEVICE_TABLES = "files/device_table-minimal.txt"
 
 LIC_FILES_CHKSUM = "file://${COREBASE}/LICENSE;md5=3f40d7994397109285ec7b81fdeb3b58 \
                     file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420 \